In recent years, displays in image display devices, such as television devices, are being shifted from conventional cathode-ray tube displays to thin displays, such as liquid crystal displays and plasma displays. With the thin displays, thicknesses of the image display devices can be decreased. Liquid crystal panels do not emit light. Therefore, liquid crystal display devices including liquid crystal panels require backlight devices. The backlight devices are classified broadly into a direct type and an edge-light type based on mechanisms. For further reduction in thicknesses of the liquid crystal display devices, the edge-light type backlight devices are more preferable. A backlight device disclosed in Patent Document 1 is known as an example of the kind.